In recent years, it has been reported that certain linear conjugated organic polymers such as poly (acetylene), poly(p-phenylene) and poly(p-phenylene sulfide), become highly conductive when properly doped. With the exception of poly(acetylene), they are crystalline but intrinsically insulating when undoped.
There have been many polymers known to be semiconductive when complexed with a relevant dopant. However, only scores of polymers are true semiconductors (.sigma.=10.sup.-3 -1 ohm.sup.-1 cm.sup.-1). Among these conductive polymers, only a handful are film- or fiber-forming semiconductors. The others are insoluble or infusible conductive solids, greatly limiting their practical potential as materials for fabricating pn junctions. Further, many polymer films, upon doping, lose their strength and flexibility.
Heteroaromatic ladder polymers of the bezimidazobenzophenanthroline type, e.g. poly[(7-oxo-7,10H-benz[de]imidazo[4',5':5,6]benzimidazo[2,1-a]isoquinoline -3,4:10,11-tetrayl)-10-carbonyl], referred to as "BBL", and poly(6,9-dihydro-6,9--dioxobisbenzimidazo[2,1-b:1',2'-j]-benzo[1 mn][3,8]phenanthroline-3,12-diyl) referred to as "BBB", have unique structures in the solid state. This type polymer has essentially two-dimensional, oriented, fully conjugated, and layered structures. Nevertheless, because a somewhat high ionization potential is expected from the amide groups in the polymer, it was hitherto not expected that this type of polymer would exhibit a high doped conductivity.